Apparatus and methods for side-fire optical fiber assembly suitable for medical applications

ABSTRACT

This invention relates to an advance in the delivery of laser beams to internal surgical sites using optical fibers with a novel distal tip design made using a fusion assembly procedure suitable for directing laser beams out of the side of an optical fiber. This side-fire fiber delivery tip assembly is fabricated by fusing a transparent tube onto the distal ends of a laser beam delivery fiber and an associated coaxial stub fiber that have beveled and parallel end faces that meet inside of the transparent tube. The result is a rugged fiber delivery tip assembly that is almost entirely solid, except for a very narrow gap between the beveled end surfaces of the two fibers. A loose fitting transparent capsule is placed over this fiber tip to contain a transparent perfluorocarbon lubricating oil or a perfluorocarbon heat-transfer agent that serves as a cooling agent for the fiber tip assembly.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional PatentApplication Ser. No. 62/252,477 filed Nov. 7, 2015, titled IMPROVEDAPPARATUS AND METHODS FOR SIDE-FIRE OPTICAL FIBER DEVICE SUITABLE FORMEDICAL APPLICATIONS and U.S. Non-Provisional patent application Ser.No. 15/338,420 filed Oct. 30, 2016, titled APPARATUS AND METHODS FORSIDE-FIRE OPTICAL FIBER DEVICE SUITABLE FOR MEDICAL APPLICATIONS thecontents of which are hereby incorporated by reference herein.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION Backgroundof the Invention

1. Field of the Invention

This invention relates to enhancement of the delivery of laser beams tointernal surgical sites, such as enlarged prostate glands (caused bybenign prostate hyperplasia, BPH) or kidney stones, using optical fibershaving a novel distal tip design for directing the laser beams out ofthe side surface of the optical fibers.

2. Description of Related Art

Over the past several decades, the medical uses of optical fibers todeliver both high and low power laser beams has substantially grown fromprimarily clinical trials to big business. One of the main drivingforces for this trend has been the ability to insert small opticalfibers into surgical cystoscopes and endoscopes to accomplish a broadrange of surgical functions within the human body such as cutting,cauterizing, and ablating of tissues and fracturing hard objects, suchas kidney stones.

At present, medical optical fiber device designs and techniques havereached a high level of development for firing a laser beam directlydown the axis of a fiber and straight out of its end to accomplish asurgical function. This geometry is referred to in this paper as“end-fire”. However, there is a class of surgical functions that canbest be accomplished by having the laser beam exit the side of a fiberrather than its end. This geometry will be referred to as “side-fire”.The side-fire technology is more complex than for end-fire and advancingthis technology is still an active field of endeavor and the subject ofthis invention disclosure.

A good example of an application where side-fire capability isbeneficial is in the treatment of BPH (benign prostatic hypertrophy). Itis relatively easy to pass an optical fiber through the ureter andposition it inside of a male patient's prostate gland. However, there isinsufficient space to make a 90-degree bend of the fiber to redirect thedistal tip of an end-fire fiber so that it is possible to ablate tissuein the surrounding prostate gland without breaking the fiber. However, aside-fire fiber is ideal for such a purpose because tissue ablation canbe accomplished without bending the fiber. The fiber remains straight,but the laser beam comes out of the side of the fiber at close to aright angle from the axis of the fiber.

In the following discussion, one should keep in mind that the mostdemanding applications for side-fire optical fibers is to deliver laserbeams with high optical power levels in the approximate range of, say,20 to 200 Watts through the limited sized channels of moderncystoscopes/endoscopes that are typically 2 to 3 mm in diameter. Thisimplies that the optical power density in the vicinity of the distal tipof the fiber will be so great that it is not only capable of performingthe desirable effects of cutting, cauterizing, and ablating humantissue, but can also be self-destructive to the fiber or fiber deliverydevice if these components are not well designed and not operated whilein competent surgical hands.

In fact, degradation to the point of inoperability is the norm forstate-of-the-art high power side-fire fiber delivery devices used inpresent surgical applications. The design objective currently desired isnot to eliminate the possibility of such degradation but to extend theuseful working lifetime of the fiber delivery device sufficiently longto accomplish a specific surgical procedure before replacement isrequired. For example, a BPH treatment typically takes approximately 15to 45 minutes to complete. So, 45 minutes is a practical minimumlifetime objective for a surgical side-fire optical fiber device inservice. A related design objective for a side-fire fiber device is todetect and alert the surgeon of incipient failure of the device beforecatastrophic failure occurs that could cause broken glass pieces fromthe fiber to be disbursed in the surgical zone and that must bepainstakingly retrieved.

Based on the above discussion, it is apparent that side-fire medicalfibers used at present fall clearly into the category of medicaldisposables that are typically used either for a single procedure or, atmost, a limited number of procedures. In fact, not infrequently, use ofmore than one side-fire fiber is required during a single procedure toavoid catastrophic failure.

While the technology that has been developed for side-fire optical fiberdevices used in medical applications is extensive, the followingdiscussion of the evolution of existing side-fire fiber tip designsestablishes that while there have been significant advances in thisfield there is still considerable room for improvement. This discussionbegins with an older unpublished U.S. patent application Ser. No.08/111,884 filed Aug. 26, 1993 titled METHOD AND APPARATUS FOR ACTIVECONTROL OF LASER ENERGY DENSITY DISTRIBUTION WITHIN A FIBER OPTICDELIVERY DEVICE that is referred to herein as Brown '884. This patentapplication introduced fresh new ideas for making practical side-fireoptical fiber devices. While this patent application has broaderapplicability than just for side-fire fibers, the discussion thatfollows is limited to the side-fire geometry.

Brown '884 recognized that it is imperative to keep the side-fire fibertip clean and cool in order to avoid thermal destruction of the fiber.The concept for accomplishing this was to insert the fiber tip with ahighly reflective optical coating applied on a beveled end surface intoa transparent and loosely fitting capillary tube filled with transparentcooling fluid, either liquid or gas. (See Prior Art FIG. 1A, below.) Thecapillary tube may be either closed or partially open at the distal end.If the bevel angle were made 45 degrees to the fiber axis, the laserbeam propagating down the axis of the optical fiber would be reflectedoff of the beveled mirror surface by an angle twice as large, 90degrees, and continue out through the side-surface of the optical fiber.

Brown '884 has very little to say about the type of cooling fluid thatshould be used inside the capillary tube. However, this patentapplication recognized the desirability that the cooling “fluid variesin optical index between the light guiding means [optical fiber] and thecapillary means [tube]”. This is in recognition of the fact thatundesired reflections of the laser beam can be minimized at theinterfaces between the optical fiber's surface and the cooling fluid andbetween the cooling fluid and the inner wall of the capillary tube bychoosing a suitable fluid. For example, if air, with an index ofrefraction of approximately 1.0 were used as the cooling fluid, opticalreflections of approximately 4% per interface would result in a total of8% reflection loss for the two interfaces associated with the outersurface of the optical fiber and the inner surface of the capillarytube. On the other hand, if a liquid, such as water with an index ofrefraction of approximately 1.33, were used as the cooling fluid, theseundesired reflections could be reduced to approximately 0.2% perinterface. And, of course, if the index matching of the cooling liquidand the fused silica in the fiber and capillary tubes were perfect(having an index of refraction of, say, 1.46), the reflections would beentirely eliminated.

Since reflected light diminishes the power of the laser beam deliveredto the surgical zone, the simple analysis above leads to preferentialuse of water or some other transparent liquid as the cooling fluidrather than a gas that would have a substantially lower refractive indexthan the optical fiber or glass in a surrounding capillary tube.However, this seemingly obvious choice of using a liquid with areasonably good refractive index match to the optical fiber material hasdire consequences if the mirror coating on the beveled tip of theoptical fiber were to fail. In that case, the laser beam would no longerbe reflected into the side-fire direction. Rather, the laser beam wouldcontinue forward in the general direction of the fiber's axis and couldcause damage and undesired necrosis to perfectly good human tissuelocated in that direction.

Unfortunately, in the years since Brown '884 was filed in 1993, no onehas succeeded in developing a reflective coating for an optical fiberthat could endure a high power laser beam required for surgicalapplications for a sufficient period to complete a procedure, such astissue ablation during BPH surgery. This represents a serious problemfor the direct use of the Brown '884 design for side-fired fibers.

Fortunately, this problem does have a solution that has been adopted inall current high powered side-fired fiber delivery designs, as discussednext. The solution was first introduced several months after Brown '884had been filed by Pon in patent number U.S. Pat. No. 5,428,699 titledPROBE HAVING OPTICAL FIBER FOR LATERALLY DIRECTING LASER BEAM referredto herein as Pon '699. The terminology “LATERALLY DIRECTING LASER BEAM”used in this title is synonymous to “side-fire”. The present inventorhas chosen to use the word “side-fire” since it describes the actualgeometry and may leave a reader with a better intuitive impression.

The Pon '699 solution to the unavailability of a durable reflectivecoating for the beveled tips of side-fire fibers is deceptively simple,just eliminate the reflective coating, yet continue to get highefficiency reflections from the beveled tip of the fiber by a processknown as total internal reflection. This is the same well known physicalprocess that is used to guide light in all optical fibers.

In fact, the solution is not so simple for two reasons. First, the spacedirectly adjacent to the beveled surface of the fiber tip must containeither a gas or a vacuum (having a refractive index of close to or equalto one). Use of a cooling liquid in that region is no longer possiblebecause its higher refractive index would “frustrate” (i.e. inhibit) thetotal internal reflection process. The second reason is that there areangular limitations for the total internal reflection process whichlimit the reflected angle to approximately 79 degrees rather than thepreferred 90 degrees. (See prior art FIG. 1B, below.) Even so, the 79degree side-fire angle has proven to be generally acceptable for lasersurgery.

A simple way to achieve such a gas or vacuum filled space adjacent tothe beveled end surface of the optical fiber is described in Pon '699. Atransparent capsule may be slid over the fiber tip and secured in placewith an optically transparent bonding agent that would resist ingress ofcooling and irrigation fluid and therefore leave an empty hollow spaceabove the beveled fiber surface (see Prior Art FIG. 1B, below). However,it was quickly learned that existing optical bonding agents exhibitedmarginal ability to survive under direct illumination of a high powersurgical laser beam. One way used to resolve this problem was torelocate the cement bond between the fiber and the transparent cap awayfrom direct illumination of the side-fired laser beam by moving itfurther down the fiber from its tip as described in U.S. Pat. No.7,909,817 B2 issued on Mar. 22, 2011 titled LATERAL LASER FIBER FOR HIGHAVERAGE POWER AND PEAK PULSE ENERGY and referred to herein as Griffin'817.

It is clear from reading Griffin '817 that moving the cement bond awayfrom direct illumination by the laser beam is only a partial solution.That is because about 4 percent of the laser beam passing out of theside surface of the fiber is reflected backwards and another 4 percentis again reflected backwards upon entry into the transparent capsule.And these reflections are highly undesirable since they inevitablyresult in substantial heating of the fiber tip region. Their origin iswell known as Fresnel reflections that are due to a refractive indexmismatch between the fused silica (use in the optical fiber and,frequently, in the capsule) and the air or vacuum within the small spacebetween the fiber side-surface and inner capsule surface. The dilemma isthat the only way to eliminate these reflections would be to fill thespace between the fiber side-surface and the capsule with a refractiveindex matching material that would, unfortunately, also fill the hollowregion above the beveled surface and frustrate the necessary totalinternal reflection of the surgical laser beam.

Griffin '817 mentions the possibility of fusing (welding) the capsuledirectly to the fiber tip to eliminate the Fresnel reflections anddescribes two such designs in U.S. Pat. No. 5,562,657 (Griffin '657) andU.S. Pat. No. 5,537,499 (Brekke '499). See, for example, Prior Art FIG.1C. below. Griffin '817 goes on to say “Both are high efficiency designsthat utilize fiber-to-cap fusion to minimize scatter. Both fail atapproximately 40 W [Watts] through catastrophic disintegration. It isthought that the residual stress concentration in the fiber-to-capfusion region likely render the fused fibers more susceptible to thethermal shocks encountered in the surgery than non-fused fibers”.

Griffin '817 also discuss several ways besides fusing to mitigate theeffects of the undesired Fresnel reflections such as applying areflective coating on the outer rear surface of the capsule to redirecta portion of the reflected light back towards the main laser beam (seeprior art FIG. 1D, below) as well as using complicated cooling channelswithin the capsule to remove the excess heat generated as a consequenceof the Fresnel reflections (see Prior Art FIG. 1E, below). However,neither method has proved to be without problems. For example, Griffin'817 states “At high average [laser] power or peak pulse energy, a gold[reflective coating on the reverse outer surface of the capsule] . . .is damaged by the highest peak energy in the reflective beam, producinga burn through spot diameter roughly ½ of the output beam diameter . . .”. And use of the complicated cooling channels in the capsule has notyet proven to be commercially viable.

A limited solution to the Fresnel reflection problem has been found byPeng et al. as described in U.S. Patent Publication No. 2009/0048585 andreferred to herein as Peng '585. This work employs a method for coolingthe fiber tip that is substantially less complex than that described inGriffin '817. Peng '585 uses a thin walled transparent capsule of verylimited diameter that fits loosely inside of an outer metal tube (seePrior Art FIG. 1F, below). This tube has hole in it that serves as aport for the side-fired laser beam. In operation, cooling fluid,typically water or saline solution, is made to flow in the gap betweenthe outer surface of the transparent capsule and the inner surface ofmetal tube and this cooling fluid exits through the same port in themetal tube as the optical beam.

This fiber tip design has functioned satisfactorily when used inconjunction with a commercially available laser, a frequency doubledNd:YAG laser, sold by Boston Scientific. Inc. that has been named theGreenLight laser due to its green, 0.532 micron wavelength, output.However, this tip design appears to be limited to use with lasers havingoutput wavelengths, like the GreenLight laser, that exhibit very lowoptical attenuation in the aqueous cooling fluid and in the organicoptical bonding agent used to secure the transparent capsule to thefiber. Hence, the Peng '585 fibers are sometimes referred to as the“GreenLight fibers” which emphasizes their limited spectral use.

Griffin '817 has pointed out that it became apparent when GreenLightfibers were used with the infrared Ho:YAG laser beam (having a 2.1micron wavelength) that the organic optical bonding agent securing thecap to the fiber tip rapidly deteriorated under infrared illumination.

A second, and more serious problem with the GreenLight fibers describedin Griffin '817 [Column 3 lines 30-35] is:

The photo-thermal and/or photoacoustic shock waves that are generated bythe [Ho:YAG] laser pulses and in the water are so intense that caps ofsimilar dimensions to those used in the PVP [GreenLight] fiber cansimply shatter to dust at average powers of 40 W or more. Thicker capsresist this damage but remain susceptible to erosion failures inapparent excess of that seen in PVP [GreenLight fiber].

To resolve the problem associated with the failed bonding agent as wellas another problem related to the immobility of the fiber tip within theGreenLight fiber cap, Griffin '817 came up with a new design using adouble cap arrangement. A very thin inner cap is fused directly onto thebare fiber end. Then, this sub-assembly is inserted into a secondarycap. (see Prior Art FIG. 1D, below). Significantly, the inner cap,containing the fiber, can be moved by the surgeon relative to the second(outer) cap so that if outer surface of the secondary cap were to becomecontaminated by surgical debris that could limit the power of the laserbeam, it would be possible to simply move the fiber (and thereby thelaser beam) to pass through a clear (unrestricted) area in the secondarycapsule. While this appears to be a reasonable approach, in principle,the complexity associated with this tip design and the lack of directcooling of the optical fiber (there remains a gap between the opticalfiber and the inside wall of the inner cap) continue to raise seriousconcern.

Clearly, it would be a desirable objective to (1) simplify the design ofside-fire fiber tips, (2) make them suitable for use with a broad rangeof surgical lasers with output wavelengths in both the visible andinfrared portions of the optical spectrum, (3) make them more rugged byeliminating the need for organic bonding agents, and (4) extend theirworking life-time so that mid-procedure replacement would no longer berequired during surgery.

SUMMARY OF THE INVENTION

This invention relates to a substantially different structure for theoptical fiber tips than those discussed above that will ensure totalinternal reflection, essential for high power side-fire optical fibertips, without the need for a relatively large hollow cavity adjacent tothe beveled fiber surface on the fiber's tip nor the need for organicbonding agents. The objective behind changing the design and fabricationmethods for the side-fire optical fiber tips is to achieve such a highlevel of function and durability that such tips will no longer fall intothe category of disposables, to be used for only a single surgicalprocedure. In addition, this invention introduces the use of atransparent perfluorocarbon lubricating oil or a perfluorocarbonheat-transfer agent that serve as cooling agents and irrigation fluidsfor the fiber tip assembly due to the inert chemical nature thesematerials and their high transparency in the infrared spectral range of1.1 to 2.2 microns where a number of surgical lasers operate.

The new design recognizes that the Prior Art designs that employtransparent capsules with thin walls and substantial hollow empty spacesover the beveled fiber tips, as described in Griffin '817, will alwaystend to be frail and problematic both in product assembly and duringsurgical use.

In contrast, the new side-fire optical fiber tip is almost entirelysolid to reduce geometrical thermal and mechanical stresses, which, inturn, produces a very robust structure. The solution of this problemcame with the realization that the empty space behind the beveled tip ofthe fiber need be only several optical wavelengths thick to adequatelyassure the function of total internal reflection. The much largervolumes that are used in the present state-of-the-art fiber tip designsare not necessary but simply a matter of convenience to simplifyassembly.

These thoughts led to a circularly-symmetric structure having a laserbeam delivery fiber with a beveled end in line with a short stub fiberalso with a beveled end. The gap between the two facing beveled fiberends can be made to be in the range of, say, 50 microns or less, thinnerthan a half sheet of paper. When a thin walled fused silica cylindricalcapillary tube is closely fit over the delivery fiber tip and the stubfiber tip and then fused (glass-to-glass) in place, the resultingstructure is entirely solid except for the narrow gap between the fibertips. No organic bonding agent is required. This robust structure willbe more completely describe in the following two sections relating tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above SUMMARY OF THE INVENTION as well as other features andadvantages of the present invention over the Prior Art will be morefully appreciated by reference to the following detailed descriptions ofillustrative embodiments in accordance with the present invention whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1A is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Brown '884.

FIG. 1B is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Pon '699.

FIG. 1C is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Brekke '499.

FIG. 1D is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Griffin '817.

FIG. 1E is another cross-sectional drawing of the Prior Art fiber tipdesign developed by Griffin '817.

FIG. 1F is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Peng '585.

FIG. 2 is a cross-sectional drawing of the new fiber tip designintroduced in this specification.

FIG. 3 is a perspective drawing of the fiber tip assembly shown in FIG.2 that is inserted into a transparent capsule (shown in cross-section)

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Brown '884. An optical fiber, 1, has a beveled end 2 thatis coated with a highly reflective coating 3. A laser beam 4 propagatingdown the axis of this fiber will reflect off of the beveled end 2 and bere-directed out though the side of the fiber. A loose fittingtransparent capsule 5 containing a transparent fluid 6 is placed overthe distal end of the beveled fiber for protection and possibly cooling.The tissue ablation zone (for example, in the case of BPH treatment) isimmediately outside of the outer wall of this capsule 5. The fiber tipcan be rotated or translated within the loose fitting transparentcapsule either manually or automatically so that if the region on thecapsule's outer surface where the laser beam passes become damaged orobscured by adherent surgical debris, a common occurrence, the surgicalprocedure can continue simply by moving the laser beam 89 to anotherposition on the capsule's surface that is not damaged. This offers asignificant advantage so that the surgical procedure may continue to asuccessful conclusion without a delay that would be required to replaceor repair the fiber tip.

Unfortunately, in the years since Brown '884 was filed in 1993, no onehas succeeded in developing a reflective coating 3 for an optical fiberthat could endure a high power laser beam required for surgicalapplications for a sufficient period to complete a high power laser beamprocedure, such as tissue ablation during BPH surgery. This represents aserious problem for the direct use of the Brown '884 design forside-fired fibers.

FIG. 1B is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Pon '699. In this case the optical fiber 11 also has abeveled end surface 12 but it has no reflective coating. Rather thelaser beam 13 is reflected from the fiber end by the well-known processof total internal reflection. This is the same well known process thatis used to guide light in all optical fibers. A gas or vacuum filledspace 16 adjacent to the beveled end surface 12 of the optical fiber isestablished by the use of a transparent capsule 14 that is slid over thefiber tip and secured in place with an optically transparent bondingagent 15 that resists ingress of cooling and irrigation fluid andtherefore leaving an empty hollow space above the beveled fiber surface16 that is necessary for the total internal reflection process to occur.However, it was quickly learned that existing organic optical bondingagents exhibited marginal ability to survive under direct illuminationof a high power surgical laser beam. One way used to resolve thisproblem was to move the bonding agent 15 between the fiber 11 and thetransparent capsule 14 away from direct illumination of the side-firedlaser beam further down the fiber from its tip to region 17.

FIG. 1C is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Brekke '499. The objective of this design is to fuse thetip 21 of the optical fiber 25 directly to the inner wall 22 of thecapsule 23 to avoid unwanted Fresnel reflections. Unfortunately, Giffin'817 has reported that the fusion joint 24 between the fiber tip 21 andcapsule 23 is susceptible to stress failure induced by a high powerlaser beam 20, shown as three parallel rays with arrows that indicate todirection of propagation of this laser beam 20.

FIG. 1D is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Griffin '817. A first capsule 41 containing an opticalfiber 42 with a beveled end 43 is inserted into a second capsule 44. Theshaded region 45 located on the outside surface of the second capsule 44represents a mirror made by depositing a reflective gold coating. Thepurpose of this coating is to re-reflect any rays from the laser beam 46that may have been reflected in the backward direction, due to Fresnelreflection, after passing through the fiber's side-wall and the innersurface of the first capsule.

FIG. 1E is another cross-sectional drawing of the Prior Art fiber tipdesign developed by Griffin '817. The fiber 51 and first (inner) capsule52 are identical to the same parts shown in FIG. 1D. However, the second(outer) capsule 53 has a series of helical cooling channels 54 machinedinto the capsule's wall using a micro machining method, possiblyemploying a CO₂ laser beam. A cooling fluid can be employed that flowsthrough the cooling channels 54 and through the cylindrical gap betweenthe first (inner) capsule 52 and the second (outer) capsule 53. Griffin'817 anticipates using non-aqueous cooling fluids (see Column 10 Lines26-34) that include fluorocarbon solvents as well as other materialsthat are not fluid or that become fluid at elevated temperatures, suchas amorphous fluoropolymers (e.g. Dupont Teflon AF 1600) and indexmatching gels.

FIG. 1F is a cross-sectional drawing of the Prior Art fiber tip designdeveloped by Peng '585. In this design, the optical fiber 61 with abeveled tip 62 is contained inside of a transparent capsule 63 which is,in turn, located inside of a loose fitting meal tube 64. The metal tube64 has a hole 65 to provide an exit port for the side-fired laser beam66. In operation, cooling water or saline solution is forced down theannular gap between the outer surface of the transparent capsule 63 andthe inner surface of the metal tube 64. This coolant eventually isexhausted through the same hole 65 in the metal tube that passes thelaser beam. It is apparent that the fiber 61 cannot be translated orrotated within the metal tube 64 because the laser beam would then missthe hole 65 and strike the inner wall of the metal tube 64.

FIG. 2 is a cross-sectional drawing of the novel side-fire fiber tip 80that is the subject of this disclosure. A rugged side-fire fiber opticaltip is made by joining together the following three components: (1) alaser beam delivery fiber 81 with a tip 82 that is beveled at an angle83 of 39.5 degrees or less relative to the fiber's axis in order tosupport total internal reflection of a laser beam 84 transmitted in thisfiber, (2) a short stub fiber 85 having the same outside diameter as thedelivery fiber 81 and that is beveled 87 at one end with the same angleas the delivery fiber, and (3) a short transparent tube 86 having aninside diameter slightly larger than the outside diameters of the twofibers 81 and 85, that are assembled together by inserting the beveledends of the delivery fiber 81 and stub fiber 85 fully into thetransparent tube 86 so that the two beveled surfaces are parallel andseparated by a narrow gap 88 followed by fusing these three componentsin place such that the small space associated with the gap between thetwo beveled fiber surfaces is hermetically sealed from the outsideenvironment. This assembly results in a rugged structure that iscompletely inorganic and solid except for the space associated with thesmall gap 88 between the delivery fiber 81 and the stub fiber 85. Theactual size of this gap must be greater than approximately 5 microns tosupport total internal reflection of the laser beam 89 and less than,say, 1,000 microns (1 mm) to ensure a rugged structure. The preferredsize range for this gap would be in the range of 10 microns, to simplifypositioning the fibers during set-up, and 100 microns to mitigate anystresses that would negatively impact durability and ruggedness of thetip structure.

After the laser beam delivery fiber, the short stub fiber and the shortsurrounding transparent tube have been fused together the length of thedistal end of the fiber tip containing the stub fiber is reduced, forexample by saw cutting or scoring and breaking, such that the finallength 79 of the distal end of the fiber tip made up of the stub fiberfused to the transparent tube is sufficient to maintain a hermetic sealfor the gap 88 between the beveled surfaces of the laser beam deliveryfiber and the beveled stub fiber but no greater than, say, 5 mm andpreferably 1 mm or less in order to allow use of the fiber tip inconstricted spaces.

Essentially all optical fibers used for laser surgery have pure fusedsilica cores that are surrounded by lower refractive index claddingsmade from fused silica that includes either a fluorine or boron oxideaddition of no greater that 5 weight percent (to reduce the refractiveindex of the cladding). So, both the core and cladding regions have ahigh silica content (95% or greater) and their thermal expansionproperties are quite well matched. In order to reduce thermally inducedstresses during the fusion assembly of the tip structure, it isadvantageous to select a capillary tube material that is also composedof 95 weight percent SiO₂, or greater. To achieve the most favorablefinal stresses in the tip structure, the capillary tube should be madeeither from pure fused silica (prepared by reacting silicontetrachloride, SiCl₄, with oxygen, O₂) or fused quartz (naturallyoccurring crystalline SiO₂ that is melted into a glassy state).Specifically, if the SiO₂ concentration in the capillary tube is greaterthan that in the cladding region of the optical fibers, a favorablecompressive stress is known to develop in the outer surface of thecapillary tube upon cooling after fusion that will tend to strengthenthe capillary tube. Here, it should be pointed out that glass (includingfused silica) never fails under compressive stress. Rather, such acompressive stress must be overcome by a larger tensile stress beforefailure even becomes possible.

The details associated with the fusion step to produce the side-firefiber optical tip structure shown in FIG. 2 are important to achieve thedesired hermetic seals between the delivery fiber and stub fiber and thecapillary tube. Without such hermetic seals on both fibers, coolingfluid and/or irrigation fluid used during surgery could migrate into thegap 88 and frustrate the total internal reflection process that isrelied upon to achieve the desired side-fire performance of the fibertip. And due to the high silica content of both fibers and the capillarytube, high temperatures are required to achieve fusion. In fact, thetemperatures are so high that there are only several options for thefusion heating source. They are (1) an oxyhydrogen flame, (2) anelectric arc, or (3) a CO₂ laser beam (or some other laser having a beamwavelength that is strongly absorbed by SiO₂). Prior to the actualfusion step, the delivery fiber and stub fiber must be carefully setinto position. During this setup, it is necessary that the insidediameter of the capillary tube is larger than the outside diameter ofthe fibers so that it is possible to insert the fibers into thecapillary tube with very little or no friction. Yet, the difference inthese diameters should be small enough so that it is unlikely to entrapgas between the fiber and capillary tube during the subsequent fusionstep. A difference in the inside diameter of the capillary and theoutside diameter of the two fibers of 100 microns or less is preferred.

Based on the limited clearance between the fibers and the capillary tubeand the generally small sizes of these parts, it is apparent that itwould be helpful to employ optical magnification and micro-manipulatorsto assist in the insertion of the fibers into the capillary tube and toverify that the gap 88 is properly set before the fusion step isinitiated. It is also helpful if the stub fiber's length prior to fusionis extended several inches so that this fiber can be easily handled bygripping the extension during insertion without inadvertently disturbingthe position of the capillary tube. Then, after fusion is completed, thestub fiber's extension can be cut back to its desired final length.

It is advantageous to accomplish the final fusion step using fixtures tohold the delivery fiber and stub fiber into alignment along a commonhorizontal axis. These fixtures should contact the fibers sufficientlyfar away from the capillary tube so that they will not overheat duringthe fusion step. Experience has shown that during fusion, it ispreferred to use a small localized heating source, smaller than thelength of the capillary tube so that the tip assembly does not tend tosag when it reaches fusion temperature. To mitigate any tendency to sag,the entire fiber tip assembly may be slowly rotated on its axis (as canbe done using a small glass working lathe) during the fusion step.However, this rotation is not essential if the hot fusion zone is keptsmall.

Experience has shown that when a fused silica tube (e.g., the capillarytube) is heated to a sufficiently high temperature it will become softand circumferential surface tension will cause the tube to decrease indiameter while the wall thickness increases. If there is a solidcylinder of fused silica (e.g., an optical fiber) loosely fit inside ofthe soft heated tube, the tube's outside diameter will eventually shrinkdown and make broad contact with the surface of the cylinder and afusion joint will form. During such a fusion step, it is preferable tofirst apply the fusion heat to the surface of either the delivery fiberor the stub fiber several millimeters away from the capillary tube. Thenthe heat zone should be progressively moved towards the capillary tube,then over the surface of the capillary tube, and finally for severalmore millimeters along the opposite fiber. This method for heating isadvantageous to ensure that any gas remaining between the surfaces ofthe fibers and the inside surface of the capillary tube will have anexit path ahead of the hot fusion zone and thereby eliminate any bubblesor un-bonded regions in the fusion joint. Use of a helium gasatmosphere, rather than air, in the vicinity of the fusion zone ishelpful because helium will be absorbed within the structure of the hotfused silica parts without a tendency to form bubbles or any othernegative effects. In some cases, more than a single fusion pass may benecessary to ensure that the capillary tube has completely collapsedonto the surfaces of the fibers and that the tube and fibers are fullybonded forming hermetic seals at both ends of the tube. After thebonding operation, the quality of the seal can be checked with a heliumleak detection test by immersing the tip assembly into a heliumatmosphere for several minutes—then removing the tip for, say, 30minutes—then inserting the tip into a helium mass spectrometer used forhelium leak detection. If the seal between the fibers and the capillarywere not hermetic, some helium gas would enter the gap region during theimmersion in the helium atmosphere and it would continue to leak out andbe detected during the subsequent leak detection test.

In order for this fiber optic tip assembly 80 to fit into the limitedchannel diameters available in surgical cystoscopes or endoscopes(typically, 2 to 3 mm in diameter) and still have space for the flow ofcooling/irrigation fluid, it is desirable to keep the outer diameter ofthe fused capillary region relatively small. This, in turn, implies arelatively thin wall thickness for the capillary tube. The preferredrange would be, say, 100 microns or greater to give the capillary tubesufficient strength for handling during tip assembly and less than 300microns so that the outside diameter of the entire tip assemblyincluding a typical 600 micron diameter optical fiber is less than, say,1,200 microns (1.2 mm).

FIG. 3 is a perspective drawing of the fiber optic tip 80 shown in FIG.2 that is inserted into a transparent capsule 91 (shown incross-section) containing a cooling/irrigating fluid 92 to form acomplete fiber optic tip assembly 90. The purpose of this capsule 91 isto provide a mechanical and optical barrier between the fiber tipassembly and the surgical site (target) 93. The side-fire laser beam 94must pass through the cylindrical wall of the capsule 91 to impinge onthe surgical site 93. Typical dimensions for capsule would beapproximately 2,000 microns (2 mm) in outside diameter, 200 micron wallthickness, and 8 to 10 mm long. This would allow for a circularlysymmetric gap between the inner surface of the capsule and the outersurface of the fiber tip assembly (assuming a 1,200 micron outerdiameter for the fiber optic tip device 90) of approximately 200microns, through which cooling/irrigation fluid could flow in thedirection of the arrows 95. The cooling/irrigation flow could pass outof an optional opening in the distal end 96 of the capsule 91. For somesurgical laser wavelengths in the visible and near infrared, shorterthan 1.1 microns, normal water or saline solution is sufficientlytransparent to be used as an irrigation fluid. For longer infraredwavelengths, including 1.47 microns, the use of heavy water or a heavywater based saline solution is preferred over normal water due to itsgreater transparency. (See U.S. Provisional Patent Application Ser. No.62/252,471 filed Nov. 7, 2015 by Douglas Pinnow and U.S. Non-Provisionalpatent application Ser. No. 15/338,423 filed Oct. 30, 2016 by DouglasPinnow both titled LASER SURGERY EMPLOYING HEAVY WATER TO ENHANCE LASERBEAM TRANSMISSION.) In some applications, it may be helpful to limit theuse of heavy water only to surround the fiber tip located inside of aclosed-ended capsule 91. In these applications, that do not include theflow of heavy water for irrigation, only a very limited amount of heavywater is required to fill the capsule to serve as a highly transparentmedium to transmit the laser beam and to provide a degree of refractiveindex matching to reduce reflections of the laser beam within thecapsule.

For surgical laser wavelengths within the range of 1.1 to 2.2 microns,use of other cooling/irrigation fluids made from perfluorocarbon liquids(wherein all C—H chemical bonds have been replaced by C—F chemicalbonds) that have been developed for high performance lubricants andheat-transfer agents that have been discovered by the inventor to beparticularly effective due to their low optical attenuation in thiswavelength range and low toxicity in humans. Examples of these fluidsinclude the Krytox® family of lubricants developed and produced byDuPont™ and the Flourinert™ Electronic Liquid heat-transfer fluidsdeveloped and produced by 3M Company (3M Electronics Markets MaterialsDivision, St. Paul, Minn.).

Krytox® is a group of colorless synthetic lubricants ofpolyhexafluoropropylene oxide, with a chemical formula:F—(CF(CF₃)—CF₂—O)_(n)—CF₂CF₃, where the molecular size is determined bythe value of “n” in this chemical formula and generally lies within therange of 10 to 60. These compounds are collectively known by many namesincluding perfluoropolyether (PFPE), perfluoroalkylether (PFAE) andperfluoropolyalkylether (PFPAE). It has been found that Krytox® compound143AZ (with a molecular weight of 1850) is preferred forcoolant/irrigation applications in laser surgery due its relatively lowviscosity, broad thermal working range (up to 149° C.) and high opticaltransparency in the 1.1 to 2.2 micron wavelength range. This wavelengthrange includes the Holmium:YAG laser operating at 2.1 microns, theThulium:YAG laser operating at a wavelength of 1.94 microns and theRaman diode pumped fiber laser operating at 1.47 microns. All of theselaser sources are important in treating BPH either individually or in asingle combined product (such as the MultiPulse Tm+1470 laser systemproduced by JenaSurgical GmbH, located in Jena, Germany. (Here, “Tm” isthe abbreviation for a Thulium laser and 1470 refers to the number ofnanometers that is equivalent to a 1.47 micron output wavelength of aRaman laser.). The inventor has discovered that the optical attenuationin Kryton® 143AZ is less than 0.06 cm⁻¹ at both the 1.47 micron (Raman)and 1.94 micron (Thulium) wavelengths. So, a single laser beam fiberdelivery apparatus employing Krytox® could be used to transmit both ofthese wavelengths.

Fluorinert™ is the trademarked brand name for the line of electronicscoolant liquids sold commercially by 3M. It is an electricallyinsulating, stable fluorocarbon-based fluid, which is used in variouscooling applications. It is mainly used for cooling electronics.Different molecular formulations are available with a variety of boilingpoints, allowing it to be used in “single-phase” applications, where itremains a liquid, or for “two-phase” applications, where the liquidboils to remove additional heat by evaporative cooling. Two examples ofFluorinert™ liquids that are particularly well suited forcooling/irrigation in laser surgical applications are 3M compounds FC-40with a boiling point of 165° C. and FC-70 (perfluorotripentylamine) thatcan be used at temperatures up to 215° C.

Both of the above types of fluorocarbons, Krytox® and Fluoroinert™ areessentially inert to animal/human ingestion. However, avoidance of eyecontact is recommended by the manufacturers. The inert nature ofFluorinert™ materials was popularized in the science fiction movie “TheAbyss” where it was postulated that divers could descend to great depthsby breathing highly oxygenated liquid Fluorinert™. Several rats wereshown in this movie actually receiving a sustaining oxygen supply bybreathing oxygenated Fluorinert™ liquid that filled an aquarium wherethey swam below the surface. However, scenes depicting actor Ed Harrisusing a fluid-breathing apparatus were only simulated.

It is significant to recognize that the tissue ablation zone (forexample, in the case of BPH treatment) is immediately outside of theouter wall of the capsule 91. And during ablation, the outer surface ofthis capillary may come in direct contact with ablated tissue debristhat can stick to this surface and become further heated by the highpower laser beam. The heating may become so intense that it can causethe tissue to deposit an adherent opaque layer onto the outer surface ofthe capillary tube due to carbonization (burning off of the oxygen andhydrogen content in the tissue and leaving a darkish carbon residue).This darkish residue will selectively absorb more of the energy in thelaser beam 94 so that if the surgical procedure is continued withoutmodification, localized heating of the capillary wall will ultimatelyoverwhelm the cooling capacity of the internal cooling fluid and thewall will likely deteriorate and, possibly, fail leading to fracturedglass and spilled cooing fluid—a very undesirable situation.

The solution to this problem is to provide a feedback mechanism, eitherto the surgeon or automatically to a controller, so that the surgicalprocedure may be either modified or terminated to avoid such acatastrophic failure. The preferred remedial procedure would be toeither translate or rotate the fiber tip assembly within the capillarytube 91 so that if the capillary tube's wall becomes obstructed in aspecific area by surgical debris, the tip assembly can be repositionedto another location where the wall is clear of such debris. This offersa significant advantage so that the surgical procedure may continue to asuccessful conclusion without the need to replace the fiber tip. Thisstrategy eliminates the concern of surgeons that their fiber tipassembly might become opaque due to build-up of carbonized tissue debrisand require replacement before an operating procedure is finished.

While motion of the fiber tip assembly relative to the capsule by asurgeon, as needed, to present a clear region of the capsule's wall tothe laser beam 94 is a viable, it is also possible to automate therelative motion so that the surgeon does not even need to be concernedwith the carbonization of tissue debris on the capsule's outer surface.The strategy would be to automatically move the capsule in a slowhelical pattern relative to the fiber tip assembly using a motor driveso that that over the course of a BPH treatment that lasts between 15and 45 minutes (depending on the mass of tissue ablated) every minute orso the laser beam would pass through to a “fresh” (clean) surface areaof the capillary. So, if during the operation, the surgeon noticed thatthe optical power level reaching the tissue targeted for removal hasbeen diminished by debris, he need only wait a minute or less for a“fresh” clear area of the capillary tube to be exposed to the laser beambefore continuing with the operation.

Based on a simple analysis, one can confirm that the laser beam diametertransmitted by a typical 600 micron core diameter fiber with a numericalaperture of 0.22 would diverge to a diameter of 1 mm at the locationwhere it exited from the exterior surface of a 2 mm diameter capsule. Ifthe length of this capsule were 8 mm, it would have a total outsidecylindrical surface area of 50 square mm (2 mm×π×8 mm=50 square mm). Andif every minute, or so, slow helical rotation of the cylinder presenteda fresh 1 mm square area to the laser beam, this rotation could continuefor 50 minutes—longer than the maximum time of 45 minutes reported forBPH treatments.

A significant consequence of employing such an automated procedure isthat fiber tip assembly would be preserved for use during subsequentprocedures and only the inexpensive capsule that could be secured to acannula would be disposable. In fact, a damaged used capsule could bequickly removed and replaced without removing the surgical fiber fromthe cannula.

While the above disclosure describes a fiber optical side-fire tipdesign and assembly method that can be beneficially used in someexemplary laser surgery procedures, these examples should merely beconsidered to be representative of many others. It is therefore to beunderstood that the scope of this invention is broader than the methodsand procedures described in the specification and following claims andthat the apparatus and methods described herein relate broadly to thedesign, assembly and use of the described side-fire fiber optic tipassembly.

The invention claimed is:
 1. A side-fire fiber optical tip assemblycomprised of a side-fire fiber optical tip which is located inside of aloosely fitting transparent capsule that is filled with a transparentheat transfer liquid that is either a perfluorocarbon lubricating oil ora perfluorocarbon heat-transfer agent in which the said side-fire fiberoptical tip is fabricated by joining together the following threecomponents: (1) a laser beam delivery fiber with a distal end that isbeveled at an angle to the fiber's axis to support total internalreflection of a laser beam transmitted in the fiber, (2) a short stubfiber of the same outside diameter as the delivery fiber and that isbeveled at one end with the same angle as the delivery fiber, and (3) ashort transparent tube having an inside diameter slightly larger thanthe outside diameters of the two fibers, that are assembled together byinserting the beveled ends of the delivery fiber and stub fiber fullyinto the transparent tube so that the two beveled surfaces are paralleland separated by a narrow gap followed by fusing these three componentsin place such that the small space associated with the gap between thetwo beveled fiber surfaces is hermetically sealed in the course offusing the outer circumferential surfaces of the said laser beamdelivery fiber and said short stub fiber to the inner surface of thesaid short transparent tube.
 2. The side-fire fiber optical tip assemblyas described in claim 1 in which all three said components of the saidside-fire fiber optical tip (the laser beam delivery fiber, the shortstub fiber, and the short transparent tube) are made from fused silicaor fused quartz containing at least 95% silicon dioxide (SiO₂).
 3. Theside-fire fiber optical tip assembly as described in claim 2 in whichthe SiO₂ concentration in the said short transparent tube is equal to orexceeds the SiO₂ concentration in the outer surfaces of the said laserbeam delivery fiber and the said short stub fiber.
 4. The side-firefiber optical tip assembly as described in claim 1 in which the beveledangle between the beveled surface and the said laser beam deliveryfiber's axis is 39.5 degrees or less.
 5. The side-fire fiber optical tipassembly as described in claim 1 in which the said narrow gap asmeasured in the axial direction between the two beveled surfaces on thesaid laser beam delivery fiber and the said short stub fiber is between5 microns and 1 mm.
 6. The side-fire fiber optical tip assembly asdescribed in claim 1 in which the said narrow gap as measured in theaxial direction between the two beveled surfaces on the said laser beamdelivery fiber and the said short stub fiber is between 10 microns and100 microns.
 7. The side-fire fiber optical tip assembly as described inclaim 1 in which the inside diameter of the said short transparent tubebefore fusing is less than 100 microns larger than the diameter of thesaid laser beam fiber delivery fiber and the short stub fiber that areboth inserted into this short transparent tube.
 8. A side-fire fiberoptical tip assembly as described in claim 1 in which the said side-firefiber optical tip is fabricated using an electric arc as the heat sourcein a helium gas atmosphere that forms a fusion zone while fusing thedistal end of the said laser beam delivery fiber and the said short stubto the inner surface of the said short transparent tube.
 9. A side-firefiber optical tip assembly as described in claim 1 that is fabricatedusing a CO₂ laser beam as the heat source in a helium gas atmospherethat forms a fusion zone while fusing the distal end of the said laserbeam delivery optical fiber and the said short stub fiber to the innersurface of the said short transparent tube.
 10. A side-fire opticalfiber tip as described in claim 1 that is fabricated by progressivelyadvancing a localized hot spot produced by any fusing source startingseveral millimeters before the junction where the said laser beamdelivery fiber enters the said short transparent tube to severalmillimeters beyond the junction where the said short stub fiber exitsthe said short transparent tube.
 11. A the side-fire optical fiber tipas described in claim 1 that is fabricated by progressively advancing alocalized hot spot produced by any fusing source starting severalmillimeters before the junction where the said short stub fiber entersthe said short transparent tube to several millimeters beyond thejunction where the said laser beam delivery fiber exits the said shorttransparent tube.
 12. A side-fire optical fiber tip as described inclaim 1 in which the length of the said short stub fiber that is fusedto the surrounding short transparent tube is reduced after fusion bycutting or by scoring and breaking such that the final length of thedistal end of the said side-fire fiber optical tip made up of the saidshort stub fiber fused to the said short transparent tube is 5 mm orless.
 13. A side-fire optical fiber tip as described in claim 1 in whichthe length of the said short stub fiber that is fused to the surroundingshort transparent tube is reduced after fusion by cutting or by scoringand breaking such that the final length of the distal end of the saidside-fire fiber optical tip made up of the said short stub fiber fusedto the said short transparent tube is 1 mm or less.